7. Project Summary/Abstract This application builds on our previous intervention work (e.g., McIntyre, 2008a, 2008b, 2013; McIntyre & Neece, 2016; Neece, 2014) and proposes a longitudinal intervention study of 230 preschool-age children (ages 3?5 years) with developmental delays (DD). Behavior problems and co-occurring parenting stress are common problems in children with DD and their families. High levels of parental stress are associated with reduced response to behavioral interventions for children with DD; yet, parenting stress is almost never directly addressed in these treatments (McIntyre & Neece, 2016). The proposed study will test the benefit of addressing parental stress prior to delivering behavioral parent training (BPT) in order to more effectively reduce child behavior problems once the intervention is delivered, as well as investigate the mechanisms through which intervention outcomes occur. The study design will use a cross-site randomized, controlled trial (RCT) of standard behavioral parent training with psychoeducation (BPT-E) compared with behavioral parent training plus mindfulness-based stress reduction (BPT-M). The sample will be drawn from Lane County, Oregon, and the Inland Empire in Southern California. All families will participate in home and laboratory assessments at baseline and home assessments immediately posttreatment, as well as at 6 months and 12 months posttreatment. Measures include standardized and validated self-report and teacher-report questionnaires, gold-standard psychological assessments, and observational measures. The primary outcome of interest is child behavior problems. Analyses will be conducted using standard normal theory regression and structural equation modeling techniques, with a particular focus on latent growth modeling. Primary intent-to- treat efficacy hypotheses comparing the BPT-E with BPT-M will be specified within a set of sequential mediation analyses. The proposed study is a cross-site RCT with a PI at each site. Dr. McIntyre (MPI, University of Oregon) has more than 15 years of experience working with children with DD and their families. Her research has focused on early intervention and prevention of behavior problems. Dr. McIntyre adapted the BPT intervention used in this study and has completed two RCTs assessing the efficacy of this intervention (R03 HD047711 and R01 HD059838). Dr. Neece (MPI, Loma Linda University) has more than a decade of experience working with children with DD, and during the past 5 years has studied the feasibility and efficacy of MBSR for a diverse sample of parents of preschool children with DD. Drs. McIntyre and Neece have engaged in collaborative research for more than 10 years and have coauthored publications focused on family factors predictive of behavioral outcomes in children with developmental disabilities.